Digital Communication - Practice Test

[#56] Amplitude shift keying is not widely used, because

(A) it is too complex

(B) is more vulnerable to noise as it does not have constant envelope

(C) it requires higher bandwidth

(D) it requires more transmitted power for same P e , compared to other modulation schemes

Correct Answer

(B) is more vulnerable to noise as it does not have constant envelope

[#57] During transmission over a communication channel, bit errors occur independently with probability p. If a block of n bits is transmitted, the probability of at most one bit error is equal to

(A) 1 - (1 - p) n

(B) p + (n - 1) (1 - p)

(C) np(1 - p) n - 1

(D) (1 - p) n + np(1 - p) n - 1

(E) 1 - (1 - p) n

(F) p + (n - 1)(1 - p)

(G) np(1 - p) n - 1

(H) (1 - p)n + np(1 - p) n - 1

Correct Answer

(D) (1 - p) n + np(1 - p) n - 1
(H) (1 - p)n + np(1 - p) n - 1

[#58] A signal having uniformly distributed amplitude in the interval (-V to + V), is to be encoded using PCM with uniform quantization. The signal to quantizing noise ratio is determined by the

(A) Dynamic range of the siqnal

(B) Sampling rate

(C) Number of quantizing levels

(D) Power spectrum of signal

Correct Answer

(C) Number of quantizing levels

[#59] Companding in PCM systems lead to improved signal to quantization noise ratio. This improvement is for

(A) Lower frequency components only

(B) Higher frequency components only

(C) Lower amplitudes only

(D) Higher amplitudes only

Correct Answer

(C) Lower amplitudes only

[#60] In binary data transmission DPSK is preferred to PSK because

(A) A coherent carrier is not required to be generated at the receiver

(B) For a given energy per bit, the probability of error is less

(C) The 180° phase shifts of the carrier are unimportant

(D) More protection is provided against impulse noise

Correct Answer

(A) A coherent carrier is not required to be generated at the receiver

Digital Communication - Study Mode

[#56] Amplitude shift keying is not widely used, because

Correct Answer

[#57] During transmission over a communication channel, bit errors occur independently with probability p. If a block of n bits is transmitted, the probability of at most one bit error is equal to

Correct Answer

[#58] A signal having uniformly distributed amplitude in the interval (-V to + V), is to be encoded using PCM with uniform quantization. The signal to quantizing noise ratio is determined by the

Correct Answer

[#59] Companding in PCM systems lead to improved signal to quantization noise ratio. This improvement is for

Correct Answer

[#60] In binary data transmission DPSK is preferred to PSK because

Correct Answer